The present disclosure relates to aircraft environmental control systems. More specifically, the present disclosure relates to a cooling air flow path to cool at least one bearing in an air cycle machine.
Air cycle machines are used in environmental control systems in aircraft to condition air for delivery to an aircraft cabin. Conditioned air is air at a temperature, pressure, and humidity desirable for aircraft passenger comfort and safety. At or near ground level, the ambient air temperature and/or humidity is often sufficiently high that the air must be cooled as part of the conditioning process before being delivered to the aircraft cabin. At flight altitude, ambient air is often far cooler than desired, but at such a low pressure that it must be compressed to an acceptable pressure as part of the conditioning process. Compressing ambient air at flight altitude heats the resulting pressured air sufficiently that it must be cooled, even if the ambient air temperature is very low. Thus, under most conditions, heat must be removed from air by the air cycle machine before the air is delivered to the aircraft cabin.
Air cycle machines typically include rotating components mounted to a tie rod and a static housing surrounding the rotating components. A number of bearings can be used to keep the rotating components in place within the static housing. The bearings can be thrust bearings, journal bearings, and/or other bearings that can use foil, air, or both to support the rotating components. During operation, the bearings can experience elevated temperatures due to friction. If the temperature gets too high, the bearings can become damaged, reducing efficiency and possibly causing the air cycle machine to fail. Therefore, it is important to ensure the bearings remain at a sufficiently low temperature.